1. Field of Invention
The present invention pertains to the field of distributed systems. More particularly, this invention relates to a specification interpreting distributed system.
2. Art Background
A distributed control system commonly includes a set of transducers and application controllers which are arranged to provide control of industrial and other applications. Typically, the application controllers execute application programs for a distributed control system. The transducers and application controllers of a distributed control system may be interconnected via a communication network.
The transducers that may be employed in a distributed control system may include sensors such as temperature sensors, pressure sensors, tachometers, etc. The transducers that may be employed in a distributed control system may also include actuators such as valves, motors, heaters etc. Application controllers in a distributed control system may be implemented with programmable logic controllers (PLCs) or computer systems.
Prior transducers usually provide a set of adjustable parameters that are associated with their transducer function. The adjustable parameters for a transducer are typically represented in terms of an object model associated with the transducer. For example, a temperature sensor provided by a particular manufacturer may have an object model that includes an adjustable sampling period parameter. A temperature sensor from another manufacturer may provide an object model that includes an adjustable sampling frequency parameter. Both of these example adjustable parameters, sampling period and sampling frequency, control the rate at which a transducer performs a measurement. That rate, however, is represented differently in the object models of the transducers.
In a prior systems, an application program that controls a transducer usually obtains the object model for the transducer using, for example, messages exchanged via a communication network that connects to the transducer. The application program then typically determines the appropriate settings for the adjustable parameters in terms of the object model. The application program may access one or more transducer databases in order to obtain additional information necessary for a particular type of transducers. The application program then usually writes the selected settings for the adjustable parameters back to the transducer.
A given distributed control system commonly employs similar types of transducers from differing transducer manufacturers. In addition, similar types of transducers from differing manufacturers commonly have differing adjustable parameters as represented in their object models. Such differing adjustable parameters and object models for similar types of transducers usually requires that an application program have the capability of handling the object models of a wide variety of transducers.
Unfortunately, the inclusion of capabilities for handling multiple and diverse object models usually increases the time and cost required to develop application programs for a distributed control system. Moreover, new types of transducers added to such a prior system usually requires that existing application programs be modified to handle any new object models. This usually increases the cost of maintaining existing control systems and may limit the market for transducer manufacturers with respect to existing systems.
In addition, similar types of transducers from differing manufacturers commonly have differing constraints among their adjustable parameters. These differing constraints further complicates the task determining the appropriate settings for the adjustable parameters of differing transducers. Such complications usually increase the time and the cost of developing application programs in prior distributed systems. These differing parameter constraints also usually complicate the task of integrating new types of transducers into existing systems.